Allow interactive parameters configuration

With this patch, when `:interactive_mode = true`, the tasks `symfony:composer:install` and `symfony:composer:update` are run in interactive mode. This allows `incenteev/composer-parameter-handler`, which is included into Symfony by default, to display the wizard to remotely configure the application parameters for the deploy target server, just like it does when a Symfony project is created locally.
When  `:interactive_mode = true`, this patch does not change the tasks' current behavior: the parameters are automatically configured using the default values found into the `.dist` file.